Gas-liquid separation equipment and systems have a long range of industrial applicability including the oil and gas industry. Subsea separation, including deep-water subsea separation, involves particular challenges with respect to weight and size of the equipment to be used.
The weight and size limitations involve challenges with compact separation systems, because the systems have to be compact with low weight. Additionally the systems should be robust, i.e. have reduced need for maintenance. The system must however be accessible for intervention.
A separation process design should be robust such that the separation process can be operated safely and reliably with respect to specifications, and also the quality of the gas and liquid outlets should be delivered in accordance with specifications. A simple and robust process design also enables conventional and robust process control configurations.
If the gas and liquid outlets are not within the quality specifications, downstream equipment such as pumps and compressors may be damaged.
The inlet flow may be uncertain and varying, both in amount and composition, and it is thus necessary that the system have good and easy turndown and start-up abilities as well as flexible operating ranges.
Operating in deep water, it is an advantage that the system can be classified and approved according to pipe code instead of pressure vessel.
Examples of multiphase separation systems are found in e.g. WO 00/40834 A1, GB 2 394 737 A and U.S. Pat. No. 6,197,095 B1.
WO 00/40834 A1 relates to a method for removing condensables from a natural gas stream at a wellhead downstream of the wellhead choke thereof. This publication discloses a method for removing condensables from a natural gas stream at a wellhead, the method comprising the steps of: (A) inducing the natural gas to flow at supersonic velocity through a conduit of a supersonic inertia separator and thereby causing the fluid to cool to a temperature that is below a temperature/pressure at which the condensables will begin to condense, thereby forming separate droplets and/or particles; (B) separating the droplets and/or particles from the gas; and (C) collecting the gas from which the condensables have been removed, wherein the supersonic inertia separator is part of the wellhead assembly downstream of the wellhead choke. WO 00/40834 A1 also discloses a device for removing said condensables from said natural gas that is part of the wellhead assembly downstream of the choke.
GB 2 394 737 A discloses a fluid separation system for separating a multiphase fluid from a well comprising at least one first gravity separator and at least one second gravity separator, and valves which allow the first and second gravity separators to be set in parallel or series formation depending on the properties of the fluid and process conditions. Valves can be selectively opened or closed to allow the first separators to operate in parallel formation followed by a secondary re-separation process through second separators which are also operated in parallel formation.
In U.S. Pat. No. 6,197,095 B1, a subsea multiphase fluid separation system and method are disclosed where the system is a modular construction and the modules are secured in a single frame to be lowered as a unit to the seabed. The system utilizes reliable cyclonic operation. The sequence of the process steps is designed to make the system more efficient as compared to surface separating systems and thereby permit a more compact size as is desirable for subsea operations. The method of operation includes up to five basic process steps, with the initial step in one embodiment including cyclonically separating solids. A second stage is directed to cyclonically removing bulk gas from the liquid in either a cyclone or auger separator. A liquid-liquid hydro-cyclone for the third stage acts to pre-separate the fluid either by separating and/or by coalescing oil droplets in a water continuous stream and/or water droplets in an oil continuous stream. A fourth stage gravity separator is significantly smaller for the flow throughput as compared to surface separating systems due to the earlier separation processes and due to the option of subsequent oil-water separation in a de-oiling liquid-liquid hydro-cyclone.